/*
 * Copyright 2002-2017 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.web.servlet.view;

import org.springframework.lang.Nullable;
import org.springframework.util.ClassUtils;

/**
 * Convenient subclass of {@link UrlBasedViewResolver} that supports
 * {@link InternalResourceView} (i.e. Servlets and JSPs) and subclasses
 * such as {@link JstlView}.
 *
 * <p>The view class for all views generated by this resolver can be specified
 * via {@link #setViewClass}. See {@link UrlBasedViewResolver}'s javadoc for details.
 * The default is {@link InternalResourceView}, or {@link JstlView} if the
 * JSTL API is present.
 *
 * <p>BTW, it's good practice to put JSP files that just serve as views under
 * WEB-INF, to hide them from direct access (e.g. via a manually entered URL).
 * Only controllers will be able to access them then.
 *
 * <p><b>Note:</b> When chaining ViewResolvers, an InternalResourceViewResolver
 * always needs to be last, as it will attempt to resolve any view name,
 * no matter whether the underlying resource actually exists.
 *
 * @author Juergen Hoeller
 * @see #setViewClass
 * @see #setPrefix
 * @see #setSuffix
 * @see #setRequestContextAttribute
 * @see InternalResourceView
 * @see JstlView
 * @since 17.02.2003
 */
public class InternalResourceViewResolver extends UrlBasedViewResolver {

    private static final boolean jstlPresent = ClassUtils.isPresent(
            "javax.servlet.jsp.jstl.core.Config", InternalResourceViewResolver.class.getClassLoader());

    @Nullable
    private Boolean alwaysInclude;


    /**
     * Sets the default {@link #setViewClass view class} to {@link #requiredViewClass}:
     * by default {@link InternalResourceView}, or {@link JstlView} if the JSTL API
     * is present.
     */
    public InternalResourceViewResolver() {
        Class<?> viewClass = requiredViewClass();
        if (InternalResourceView.class == viewClass && jstlPresent) {
            viewClass = JstlView.class;
        }
        setViewClass(viewClass);
    }

    /**
     * A convenience constructor that allows for specifying {@link #setPrefix prefix}
     * and {@link #setSuffix suffix} as constructor arguments.
     *
     * @param prefix the prefix that gets prepended to view names when building a URL
     * @param suffix the suffix that gets appended to view names when building a URL
     * @since 4.3
     */
    public InternalResourceViewResolver(String prefix, String suffix) {
        this();
        setPrefix(prefix);
        setSuffix(suffix);
    }


    /**
     * This resolver requires {@link InternalResourceView}.
     */
    @Override
    protected Class<?> requiredViewClass() {
        return InternalResourceView.class;
    }

    /**
     * Specify whether to always include the view rather than forward to it.
     * <p>Default is "false". Switch this flag on to enforce the use of a
     * Servlet include, even if a forward would be possible.
     *
     * @see InternalResourceView#setAlwaysInclude
     */
    public void setAlwaysInclude(boolean alwaysInclude) {
        this.alwaysInclude = alwaysInclude;
    }


    @Override
    protected AbstractUrlBasedView buildView(String viewName) throws Exception {
        InternalResourceView view = (InternalResourceView) super.buildView(viewName);
        if (this.alwaysInclude != null) {
            view.setAlwaysInclude(this.alwaysInclude);
        }
        view.setPreventDispatchLoop(true);
        return view;
    }

}
